Two-position phase-matching device for electronic ovens



Sept. 15, 1970 J. E. STAATS 3,529,114

TWO-POSITION PHASE-MATCHING DEVICE FOR ELECTRONIC OVENS Filed Oct. 25,1968 4 Sheets-Sheet 2 was "if 1 '2 J. E. STAATS TWO-POSITIONPHASE-MATCHING DEVICE FOR ELECTRONIC OVENS Filed 001'.- 25, 1968 4$heetsSheet :5

Sept. 15, 1970 I J. E. STAATS 3,529,114

TWO-POSITION PHASE-MATCHING DEVICE FOR ELECTRONIC OVENS Filed Oct. 25,1968 4 Sheets-Sheet 4.

FIG, 7

United States Patent U.S. Cl. 219-1055 23 Claims ABSTRACT OF THEDISCLOSURE An electronic oven is disclosed including a cooking cavityand a source of microwave energy coupled thereto by a coaxial-typetransmission line the inner conductor of which comprises twospaced-apart sections defining therebetween a gap of a predeterminedlength, and a twoposition phase-matching apparatus including twoelectrically conductive members of diiferent lengths not less than thepredetermined length for phase matching the source to the cooking cavitywhen either thawed or frozen foods are disposed therein by bridging thegap with one or the other of the conductive members respectively whenthe apparatus is in its first or second positions.

The present invention relates to electronic or microwave ovens, andespecially to transmission lines for coupling a source of high frequencyelectromagnetic wave energy to a cooking cavity. In particiular, thisinvention relates to phase-matching devices for such transmission linesfor phase matching the source to the cooking cavity.

It is an important object of this invention to provide an electronicoven including a cooking cavity, a generator of high frequencyelectromagnetic wave energy and a transmission line coupling thegenerator to the cooking cavity, and which is capable of effectivelyheating both thawed foods and frozen foods.

It is another object of this invention to provide an electronic ovenincluding a cooking cavity for heating both thawed foods and frozenfoods and a generator for generating high frequency electromagnetic waveenergy and a transmission line coupling the generator to the cookingcavity and phase-matching apparatus having first and second conditionsrespectively phase matching the source to the cooking cavity when eitherthawed foods or frozen foods are disposed therein.

In connection with the foregoing object, it is another object of thisinvention to provide an electronic oven of the character describedwherein the transmission line has a hollow outer conductor surroundingan inner conductor, said inner conductor having a gap therein betweenthe generator and the cooking cavity of a predetermined length, andwherein the phase-matching apparatus has first and second positions andincludes two electrically conductive members of different lengths notless than the gap length, one of the members bridging the gap when thephase-matching apparatus is in its first position and the other of themembers bridging the gap when the phase-matching apparatus is in itssecond position.

In connection with the foregoing object, it is yet another object ofthis invention to provide an electronic oven of the character describedwherein the phase-matching apparatus includes a support member extendinginto the gap and being movable between a first position and a secondposition and two electrically conductive contact members of differentlengths not less than the gap length mounted on the support member anddrive means for moving the support member between the first and secondpositions thereof.

In connection with the foregoing object, still another object of thisinvention is to provide an electronic oven 3,529,114 Patented Sept. 15,1970 of the character described wherein the support member is anelongated rod extending through the gap normal to the longitudinal axisof the transmission line adjacent to the gap, and wherein one of theconductive members has a first length slightly greater than the gaplength and is mounted on the rod intermediate the ends thereof and theother contact member has a second length greater than the first lengthand exceeding the gap length by a length no greater than one half of thewave length of the operating frequency of the generator and is mountedon the rod adjacent to one end thereof and wherein the drive means isconnected to the rod adjacent to the other end thereof.

In connection with the foregoing object, a still further object of thisinvention is to provide an electronic oven of the character describedwherein one of the contact members has a first length not less than thegap length and is mounted on the rod adjacent to one end thereof andwherein the other contact member has a second length greater than thefirst length and exceeding the gap length b a length no greater than onehalf of the wavelength of the operating frequency of the generator andis mounted on the rod intermediate the ends thereof.

Another object of this invention is to provide, for use in an electronicoven, a phase-matching apparatus including a transmission line having ahollow outer conductor surrounding an inner conductor for transmittinghigh frequency electromagnetic wave energy, said inner conductor havinga gap therein of a predetermined length, and two-position bridging meansincluding two electrically conductive contact members of differentlengths not less than the predetermined length for bridging the gap withone or the other of the contact members respectively when the bridgingmeans is in the first or second position thereof, whereby changing theposition of the bridging means serves to change the effective electricallength of the transmission line to accomplish a shifting of the phase ofthe high frequency electromagnetic wave energy transmitted therealong.

In connection with the foregoing object, it is another object of thisinvention to provide a phase-matching apparatus of the characterdescribed wherein the bridging means includes an elongated rod extendingthrough the gap normal to the longitudinal axis of the transmission lineadjacent to the gap and being movable between a first and secondposition and wherein a first one of the contact members has a firstlength slightly greater than the gap length and is mounted on the rodintermediate the ends thereof and wherein a second one of the contactmembers has a second length exceeding the gap length by a length nogreater than one-half of the wavelength of the predetermined frequencyand is mounted on the rod adjacent to one end thereof and wherein theapparatus further includes drive means connected to the rod adjacent tothe other end thereof for moving the rod between the first and secondpositions thereof.

In connection with the foregoing object, it is other object of thisinvention to provide phase-matching apparatus of the character describedwherein the first contact member has a first length not less than thegap length and is mounted on the rod adajacent to one end thereof andwherein the second contact member is mounted on the rod intermediate theends thereof.

The invention, both as to its organization and method of operationtogether with further objects and advantages thereof, will best beunderstood by reference to the following specification taken inconnection with the accompanying drawings, in which:

FIG. 1 is a perspective view of an electronic oven according to theinvention, portions thereof being shown in broken lines;

FIG. 2 is a schematic and diagrammatic illustration of an electronicoven according to the invention showing the controls for thephase-matching apparatus;

FIG. 3 is a sectional view of the phase-matching apparatus according toa first embodiment of this invention shown, in the position for use withfrozen foods;

FIG. 4 shows the apparatus of FIG. 3 in the position for use with thawedfoods;

FIG. 5 is a sectional view of a second embodiment of the phase-matchingapparatus according to the invention shown in the position for use withthawed foods;

FIG. 6 is a view of the apparatus of FIG. 5 shown in the position foruse with frozen foods; and

FIG. 7 is a graph plotting several operating characteristics of themicrowave generator for the oven according to this invention with theloading characteristics of several types of foods superimposed thereon.

Referring now to the drawing, in particular to FIG. 1 thereof, there isshown an electric range generally designated by the numeral 70 includingtherein an electronic oven 72 according to the invention which comprisesa cooking cavity 75, a generator 80 for generating high frequency ormicrowave electromagnetic wave energy, a transmission line 85interconnecting the cooking cavity 75 and the microwave generator 80 anda phase-matching device 100. The range 70 is defined by an upstandingsubstantially box-like wall structure generally designated by thenumeral 90, including a top wall, a bottom wall, a front wall, a backwall, and a pair of opposed side walls. The front wall is provided witha front door 92 movable between a substantially vertical closed positionand a substantially horizontal open position and opening into thecooking cavity 75. For this purpose there is provided on the door 92 ahandle 94. Supported by the top wall of the range 70 is plurality orsurface heating units generally designated by the numeral 95, whichheating units 95 are preferably of the sheathed resistance conductortype.

Connected to one end of the transmission line 85 adjacent to the cookingcavity 75 and extending thereinto is an antenna structure 89 forradiating microwave energy into the cooking cavity 75.

A suitable source of microwave energy for use in operating the microwaveoven 72 is shown in FIG. 1 of the drawing and is generally designated bythe numeral 80. One preferred source of microwave energy is a crossedfield electron discharge device in the form of a multiple cavitymagnetron device of the type illustrated and described in US Pat. No.3,377,562 which issued on Apr. 9, 1968 to James E. Staats. The magnetrondevice described in that patent is particularly well suited forincorporation in electronic cooking apparatus such as the microwaveheating oven 72 of the present invention. More particularly, thismagnetron device is designed to oscillate at an ultra high frequency ofabout 915 mhz., employing anode-cathode voltages in the general range250* to 1,000 volts DC. with corresponding R.F. power outputs in thegeneral range 80 to 2,400 watts. Specifically, at a plate voltage ofabout 290 volts D.C., this magnetron device has a continuous RF. poweroutput of about 100 watts at the ultra high frequency of 915 mhz.; at aplate voltage of about 570 volts DC, this magnetron device has acontinuous RF. power output of about 700 watts at the ultra highfrequency of 915 mhz.; and at a plate voltage of about 1,000 volts DC,this device has a peak R.F. power output of about 2,400 watts at theultra high frequency of 915 mhz.

By using suitable control and power supply systems, which are alsodescribed in detail in the aforementioned US. Pat. No. 3,377,562, theabove-described magnetron device can be readily operated from the usualhousehold three-wire Edison network of 236 volts single-phase, 60-cycles AC.

The microwave energy produced by the generator 80 is coupled to thecooking cavity 75 by the transmission line 85. The transmission line 85is preferably of the coaxial type having a hollow outer conductorsurrounding an inner conductor. The inner conductor may be either hollowor solid, but is preferably solid, and both the outer conductor andinner conductor may have either a rectangular or circular cross section,as long as each has the same shape cross section.

Disposed in the transmission line between the generator 80 and thecooking cavity 75 is a phase-matching device 100, which will now bedescribed in detail. Referring to FIGS. 3 and 4 of the drawing, there isshown a two-position phase-matching apparatus according to a firstembodiment of this invention. The apparatus 100 is shown in connectionwith a transmission line 85 including a hollow outer conductor 86preferably being substantially rectangular in cross section andsurrounding a solid inner conductor 88 which has a thin straplike shapeof rectangular cross section. The outer conductor 86 has a first opening101 therein. The opening 101 may be either circular or rectangular inoutline, but is preferably rectangular. Covering the opening 101 is anouter conductor section designated by the numeral 102 which may beeither box-like or cylindrical in shape, but is preferably box-like. Theouter conductor section 102 includes a top portion 103 integral with anddisposed substantially normal to side walls 104 at one end thereof. Theside walls 104 extend outwardly from the outer conductor 86substantially normal to the longitudinal axis thereof and are supportedthereon by supporting flanges 105 which are integral with and extendoutwardly from and normal to the side walls 104 at the other endsthereof. The outer conductor section 102 thereby defines a housingcovering the opening 101. The inner conductor 88 comprises two sections'106 and 107, terminating respectively at up turned end flanges 108 and109, defining therebetween a gap of a predetermined length generallydesignated by the numeral 110. The inner conductor section 106 isseparated from and supported upon the outer conductor 86 by acylindrical insulating spacer 111 fastened therebetween adjacent to theinner conductor section end 108 by suitable fastening means 112. Theinner conductor section 107 is similarly separated from and mounted uponthe outer conductor 86 by an insulating spacer 113 fastened therebetweenadjacent to the inner conductor section end 109 by fastening means 114.

The outer conductor 86 has a second opening 115 therein disposed on theopposite side of the outer conductor 86 from the opening 101 and coaxialwith the opening 101 and the gap 110. The opening 115 is preferablycircular in outline and is substantially smaller in area than theopening 101.

A support member 120 comprising an elongated rod of circular crosssection is disposed through the openings 101 and 115 and the gap and iscoaxial therewith. One end of the rod 120 extends into the outerconductor section 102 and the other end extends outwardly beyond theouter conductor 86. The rod 120 is axially movable between first andsecond positions. A first contact member generally designated by thenumeral 125 is mounted on the rod 120 intermediate the ends thereof. Thecontact member 125 includes an insulating mounting portion 126substantially annular in shape and connected to the rod 120. Surroundingthe mounting portion 126 and attached thereto is an electricallyconductive contact portion 128 which is a thin, flat plate, preferablyrectangular in shape. The longitudinal extent of the contact portion 128is slightly greater than the length of the gap 110. The contact member125 is disposed between the outer conductor 85 and the inner conductor88 adjacent to the opening 115. Disposed on the outer side of thecontact portion 128 is an annular stop element 129 having an outerdiameter greater than the diameter of the opening in the outer conductor86. The stop member 129 is arranged to bear against the inner surface ofthe outer conductor 86 adjacent to the opening 115 when the rod is in afirst one of its two positions to prevent further outward axial movementof the rod 120. A second contact member generally designated by thenumeral 130 is connected to the rod 120 at the end thereof which extendsinto the outer conductor section 102. The contact member 130 issubstantially U-shaped and is made of an electrically conductivematerial. The contact member 130 has a flat straplike shape rectangularin cross section and is bent to form a bight 131, a pair ofsubstantially parallel legs 132 and 133 integral with and disposedsubstantially normal to the bight 131 and a pair of guide flanges 134and 135 bent slightly inwardly toward one another at the free ends ofthe legs 132 and 133. The end of the rod 120 which extends into theouter conductor section 102 has a portion 136 which is reduced indiameter and externally threaded. The contact member 130 is attached tothe rod 120 at the threaded portion 136, the bight 131 having acentrally positioned opening therethrough into which is fitted thethreaded end 136. A nut 137 secures the contact member 130 to the rod120. The contact member 130 is so attached to the rod 120 that the legs132 and 133 extend toward the gap 110 so as to respectively contact theinner conductor section ends 108 and 109 when the rod 120 is in itsfirst position.

Attached to the other end of the rod 120 externally of the outerconductor 86 is a drive means generally designated by the numeral 140.The drive means 140 includes an annular bearing bracket generallydesignated by the numeral 141 which is substantially cylindrical inshape and is disposed in surrounding relationship to the rod 120adjacent to the outer end thereof. The bearing bracket 141 includes anannular side wall 142 surrounding and coaxial with the rod 120 andhaving at the outer end thereof integral therewith and disposedsubstantially normal thereto an inwardly extending annular flange 143and having at the inner end thereof integral therewith and disposedsubstantially normal thereto an outwardly extending annular mountingflange 144. The mounting flange 144 is fastened to the outer surface ofthe outer conductor 86 so that the bearing bracket 141 overlies theopening 115 in the outer conductor 86. The plate 142 has a centrallypositioned circular opening 145 therein substantially the same size asthe coaxial with the opening 114. The drive means 140 further includes asubstantially annular retaining bracket generally designated by thenumeral 146. The retaining bracket 146 includes a side wall 147surrounding and coaxial with the side wall 143 of the bearing bracket141 and extending outwardly therefrom beyond the plate 142. At the outerend of the side wall 147 is an annular flange 148 disposed substantiallynormal to the side wall 147 and integral therewith and defining acircular opening 149 therethrough. The inner end of the side wall 147abuts the mounting flange 144 of the bearing bracket 141. Disposedwithin the retaining bracket 146 is an annular solenoid coil 150 whichextend from the plate 143 of the bearing bracket 141 axially outwardlyto the flange 148 of the retaining bracket 146. Surrounding that portionof the rod 120 which extends through the opening 115 in the outerconductor 86 and outwardly therefrom is an insulating sleeve 152. Therod 120 and the sleeve 152 extend outwardly through the opening 145 inthe plate 142 of the bearing bracket 141. Surrounding that portion ofthe rod 120 which extends outwardly beyond the bearing bracket 141 anddisposed within the annular coil 150 is a coil spring 154. A retainingnut 155 having a diameter slightly greater than the outer conductor ofthe coil spring 154, but less than the inner diameter of the solenoidcoil 150 is attached to the rod 120 at the outer end thereof. Theretaining nut 155 serves to retain the coil spring 154 within the coil150 when the rod 120 is in its first position.

In operation, when in the position shown in FIG. 3 the rod 120 ismaintained in this position by the biasing force of the coil spring 154against the retaining nut 155. In this position the stop element 129bears against the inner surface of the outer conductor 86 to preventfurther outward axial movement of the rod under the biasing action ofthe spring 154. Also, in this position the guide flanges 134 and 135 atthe free ends of the legs 132 and 133 extend into the gap 110 and thelegs 132 and 133 respectively contact the inner conductor section endflanges 108 and 109 at points 156 and 157, thus completing anelectrically conductive path from the inner conductor section 107 alongthe contact member 130 to the inner conductor section 106. In thisposition the contact member does not contact the inner conductor sectionends 106 and 107. The length along the contact member from innerconductor section end 108 to inner conductor section end 109 is such asto properly phase match microwave generator 80 to the cooking cavity 75when frozen foods are disposed therein.

The solenoid coil is energized from an electrical source to be describedhereinafter. When so energized, the rod 120, which is the plunger of thesolenoid, is moved inwardly under the action of the magnetic fieldgenerated by the solenoid to the position shown in FIG. 4. In thisposition the retaining nut 155 compresses the spring 154 against theretaining bracket 141. The contact portion 128 of contact member 125comes in contact with each of the outer conductor section ends 108 and109, thereby electrically bridging the gap 110. Also, in this positionthe contact member 130 is disposed out of engagement with the innerconductor section ends 108 and 109. The distance along the contactportion 128 from the inner conductor section end 109 to the innerconductor section end 108 is such as to properly phase match thegenerator 80 to the cooking cavity 75 when thawed foods are disposedtherein.

Re-ferring now to FIGS. 5 and 6 of the drawing, there is shown atwo-position phase-matching apparatus 200 according to a secondembodiment of this invention. The phase-matching apparatus 200 is showndisposed in a transmission line including a hollow outer conductor 96and a solid inner conductor 98, each of which has a circular crosssection. The inner conductor 98 comprises a pair of sections 206 and 207terminating respectively in a pair of flattened ends 208 and 209defining therebetween a gap of a predetermined length generallydesignated by the numeral 210. Surrounding the inner conductor section206 adjacent to the end 208 thereof is an annular insulating spacer 211which serves to center the inner conductor section 206 within the outerconductor 96. Similarly, an annular insulating spacer 213 surroundsinner conductor section 207 adjacent to end 209 thereof. The outerconductor 96 has an opening 215 therein which is generally circular inoutline. Connected to the outer conductor 96 in surrounding relationshipwith the opening 215 is an annular outer conductor section 216 whichextends outwardly from the outer conductor 96 substantially normal tothe longitudinal axis thereof adjacent to the opening 215. Disposedwithin the outer conductor section 216 adjacent to the outer end thereofis an annular insulating spacer 218 having a centrally positionedcircular opening 219 therein.

A support member 220 in the form of an elongated rod is disposed in theouter conductor section 216 coaxially therewith, one end thereofextending inwardly into the gap 210 and the other end thereof extendingoutwardly through the opening 219 in the insulating spacer 218 andtherebeyond. The rod 220 is axially movable between a first position anda second position to be defined hereinafter. Attached to the rod 220 atthe inner end thereof is a first contact member generally designated bythe numeral 225 which comprises an electrically conductive thinstrap-like member bent to form a flat elongated portion 226 and a pairof end flanges 227 integral therewith and disposed substantially normalthereto and each extending in the same direction. The distance along thecontact member 225 between the outer surfaces of the end flanges 227 issubstantially equal to and not less than the length of the gap 210'. Theinner end of the rod 220 has a threaded portion 228 of reduced diameterwhich is fitted through a suitable centrally positioned opening in thecontact member 225. A nut 229 securely fastens the contact member 225 tothe rod 220. The contact member 225 is fastened to the rod 220- so thatthe end flanges 227 extend outwardly toward that portion of the outerconductor 96 which is directly opposite the opening 215. Attached to therod 220 intermediate the ends thereof is a second contact membergenerally designated by the numeral 230 and being substantiallyU-shaped. The contact member 230 is formed from an electricallyconductive thin strap-like material of rectangular cross section whichis bent to form a bight 231 and a pair of substantially parallel legs232 and 233 integral therewith and disposed substantially normalthereto. At the free ends of the legs 232 and 233 are a pair of endflanges 234 and 235 respectively integral with the legs 232 and 233 andextending outwardly therefrom substantially normal thereto. The bight231 has a centrally positioned circular opening therein accommodatingthe rod 220 therethrough and is connected to the rod 220 thereat. Thecontact member 230 is so connected to the rod 220 that the legs 232 and233 extend inwardly toward the gap 210. The distance between the outerends of the end flanges 234 and 235 is slightly greater than the lengthof the gap 210'.

Coupled to the rod 220 adjacent to the outer end thereof is a drivemeans generally designated by the numeral 240. The drive means 240includes a bearing bracket generally designated by the numeral 241 whichis substantially annular in shape and surrounds the rod 220 adjacent tothe outer end thereof. The bearing bracket 241 includes an annular sidewall 242 surrounding and coaxial with the rod 220 and having at theouter end thereof integral therewith and disposed substantially normalthereto an inwardly extending annular flange 243 and having at the innerend thereof integral therewith and disposed substantially normal theretoan outwardly ex tending annular mounting flange 244. The flange 244 isconnected to the outer conductor section 216 at the outer edge thereof.The annular flange 242 defines an opening 245 therethrough coaxial withand of substanitally the same diameter as the opening 219 in theinsulating spacer 218 and accommodating the outer end of the rod 220therethrough. An annular retaining bracket 246 surrounds the bearingbracket 241. The retaining bracket 246 includes an annular side wall 247surrounding and contacting the outer surface of the bearing bracket sidewall 242 and extending outwardly beyond the flange 243 thereof. Theinner end of the side wall 247 abuts and is connected to the mountingflange 244 of the bearing bracket 241. At the outer end of the side wall247 is an inwardly extending annular flange 248 defining a circularopening 249 therethrough. An annular solenoid coil 250 is disposedWithin the retaining bracket 246 and extends axially between the flange243 of the bearing bracket 241 and the flange 248 of the retainingbracket 246. Disposed within the bearing bracket 241 and surrounding therod 220 is an annular stop member 253-, having an outer diameter greaterthan the diameter of the openings 219 and 245. Disposed within theannular solenoid coil 250 and surrounding that portion of the rod 220which'extends outwardly beyond the flange 243 of the bearing bracket 241is a coil spring 254. Attached to the rod 220 at the outer end thereofis a retaining nut 255 having an outer diameter less than the innerdiameter of the solenoid coil 250, but not less than the outer diameterof the spring 254.

In operation, when the rod 220 is in the position shown in FIG. thesolenoid coil 250' is not energized and the rod 220 is maintained in theposition shown by the biasing action of spring 254 against the retainingnut 255. In this position, the flanges 227 of the contact member 225respectively contact the inner conductor section ends 208 and 209 at thepoints 258 and 259, and the contact memher 230 does not contact theinner conductor 98. The distance along the contact member 225 betweeninner conductor section ends 208 and 209 is such as to properly phasematch the generator to the cooking cavity 75 when thawed foods aredisposed therein. When the solenoid coil 250 is energized by means to bedescribed hereinafter, the rod 220 which acts as the plunger of thesolenoid is moved into the position shown in FIG. 6. In this positionthe spring 254 is compressed against the flange 243 of bearing bracket241 by the retaining nut 255 and the stop member 253 bears against theouter surface of the insulating spacer 218 thereby preventing furtherinward axial movement of the rod 220. Also, in this position the flanges234 and 235 of the contact member 230 respectively contact the innerconductor section ends 208 and 209 at the points 256 and 257, and thecontact member 225 is out of engagement with the inner conductor 98. Thedistance along the contact member 230 between the inner conductorsection ends 208 and 209 is such as to properly phase match thegenerator 80 to the cooking cavity 75 when frozen foods are disposedtherein.

Referring now to FIG. 2 of the drawing, there is shown a schematic anddiagrammatical illustration of the control mechanism for thephase-matching apparatus 100. The microwave generator 80 is shownconnected to a source of electrical power of the three-wire Edison typeincluding a neutral line N that is electrically connected to groundpotential, and a pair of outside lines L1 and L2 that are electricallyinsulated from each other and from the neutral line N, each of the threelines being connected to an insulating terminal block 301. The lines L1and L2 are connected to the surface heating units by a pair ofconductors 302 and 303. The microwave generator 80 has a pair of inputterminals 304 and 305 respectively connected to the lines L1 and L2, anda pair of output terminals 306 and 307 which are connected to thetransmission line 85 through a capacitive coupling 308. In particular,the output terminal 306 is connected to the outer conductor 86 of thetransmission line 85 as at 309 and the output terminal 307 is connectedto the inner conductor 88 of the transmission line 85. The innerconductor 88 is connected through the phase-matching apparatus to theantenna 89 and the outer conductor 86 is connected to the wall of thecooking cavity 75 as at 76. The wall of the cooking cavity 75 isgrounded as at N. The phase-matching apparatus 100 is moved between itsfirst and second positions by solenoid 310 which is electricallyconnected to the line L2 by the conductors 311 and 312. The solenoid 310is mechanically coupled to the phase-matching apparatus 100 by plungerrod 315 which corresponds to the rods and 220 in FIGS. 3 through 6. Thesolenoid 310 is energized through a selector switch generally designatedby the numeral 320. The selector switch 320 includes an outer knob ordial 321 connected by a rotatable shaft 322 to insulator 323, theinsulator 323 mechanically contacting a movable contact 325. Uponoperation of the knob 321 to the position marked C, the insulator 323 isrotated by means of shaft 322 against the contact 25 thereby moving thecontact 325 into connection with the fixed contact 326 therebycompleting an electrical circuit from the line L2 to line N along theconductor 311, switch contacts 325 and 326, conductor 312 and thesolenoid 310, and thereby energizing the solenoid. Upon being soenergized the plunger 315 is moved from a first position shown to asecond position. thereby moving one contact member of the phase-matchingapparatus 100 out of engagement with the inner conductor 8S and movingthe other contact member into contact therewith. The dial 321 carrieslegends thereon C and T indicating respectively the cook and thawpositions. In the thaw position, as illustrated in FIG. 2 the switch 320is open and the solenoid 310 is unenergized and the contact member is incontact with the inner conductor 88 and transmission line 85. In thisposition the generator 80 is essentially phase matched to the cookingcavity 75 when frozen foods are disposed therein, thus enabling heatingof such foods in order to thaw them. Once thawed, the moisture in thefood is in the liquid state thereby creating a mismatch between thegenerator 80 and the cooking cavity 75. The dial 321 may now be moved tothe cook position for heating the thawed food. In this position theswitch 320 is closed and the solenoid 310 is energized thereby movingthe plunger 315 into its second position shown in FIG. 4 wherein thecontact member 130 is out of engagement with the inner conductor 88 andthe contact member 125 is connected therewith across the gap 110. Inthis position the generator 80 is properly phase matched to the cookingcavity 75 when thawed foods are disposed therein.

While FIG. 2 has illustrated the operation of the first embodiment ofthe phase-matching apparatus 100 as shown in FIGS. 3 and 4 of thedrawing, the embodiment of FIGS. 5 and 6 may be operated in a completelyanalogous manner, the only difference being that the cook and thawpositions on the dial 321 would be reversed.

Referring now to FIG. 7 of the drawing, there is shown a performancechart for the microwave generator 80 used with 50 ohm transmission linein the electronic oven of this invention, the chart comprising a Riekediagram superimposed upon a Smith chart. The data shown was obtainedutilizing a series magnetic field in the generator 80 with an applied B+potential of approximately 580 volts. As illustrated, a family of powercurves 60 was obtained, the members of the family of curves 60 for 300watts, 400 watts, 500 watts, 600 watts, 700 watts and 750 watts havingbeen illustrated. A family of curves 61 showing the frequency ofoperation, has also been plotted. Superimposed upon these curves are aplurality of load lines 63 to 66, respectively indicating the loadingcharacteristics of pork, beef, frozen foods and vegetables when thesefoods are disposed within the cooking cavity 75. As can :be seen fromFIG. 7, the loading characteristics of thawed meat loads disposed in thecooking cavity 75 are roughly centered about a radial line 67 in thephase octant between lambda and lambda. It can also be seen that theradial line 67, if extended through the center of the Smith chart willpass through the load lines 65 for frozen foods, thus indicating a phasemismatch of almost 180 degrees between a frozen load and a normal thawedmeat load in the cooking cavity 75. Accordingly, when the transmissionline 85 is of such a length as essentially to phase match the generator80 with the cook-' ing cavity 75 when thawed meat loads are disposedtherein, there will be a rather severe phase mismatch if frozen foodsare disposed in the cooking cavity 75 resulting in ineflicient heatingof the frozen foods. In particular, it can be seen from FIG. 7, thatwhen the length of transmission line 85 is set properly to match thawedloads to the generator 80, between 700 watts and 750 watts of power willbe delivered to the thawed meat loads while only a little more than 300watts would be delivered to a frozen food load. Thus, by using thetwo-position phase-matching apparatus 100 or 200 of this invention, thisserious problem of phase mismatching is substantially alleviated. Moreparticularly, by use of the phase-matching device of the invention thefrozen food load line 65 can be effectively transformed as at 63 to thephase octant occupied by the thawed meat load lines 63 and 64.

From the foregoing it will be seen that there has been provided animproved electronic oven including a microwave generator and a cookingcavity and a transmission line for coupling the microwave energy fromthe generator to the cooking cavity, and are as compatible of eflicientheating both thawed and frozen foods. More particularly, there has beenprovided an improved two-position phase-matching apparatus for changingthe effective electrical length of the transimssion line for changingthe effective electrical length of the transmission line for phasematching the generator to the cooking 10 cavity when thawed foods aredisposed therein when the phase-matching apparatus is in one positionand for phase matching the generator to frozen food load in the cookingcavity when the phase-matching apparatus is in its other position.

While there have been described what are at present considered to be thepreferred embodiments of this invention, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. In an electronic oven, structure defining a cooking cavity forheating both thawed foods wherein the water content thereof is in theliquid state and frozen foods wherein the water content thereof is inthe solid state, a generator for generating high frequencyelectromagnetic wave energy, a transmission line coupling said generatorto said cooking cavity and including a hollow outer conductor and aninner conductor, said inner conductor having a gap therein between saidgenerator and said cooking cavity, said gap having a predeterminedlength, twoposition bridging means including two electrically conductivemembers of different lengths not less than said predetermined length,said bridging means in the first position thereof bridging said gap withone of said conductive members for essentially phase matching saidgenerator and said cooking cavity when thawed foods are disposed in saidcooking cavity, said bridging means in the second position thereofbridging said gap with the other of said conductive members foressentially phase matching said generator and said cooking cavity whenfrozen foods are disposed in said cooking cavity, whereby to provideproper phase matching between said generator and said cooking cavityboth when thawed foods are disposed in said cooking cavity and whenfrozen foods are disposed in said cooking cavity.

2. The oven as set forth in claim 1 and further including a selectormechanism for actuating said bridging means between the first and secondpositions thereof, said selector mechanisms comprising a solenoidmechanically coupled to the said bridging means and a two-positionselector switch and a source of electrical current electrically coupledto said solenoid through said selector switch.

3. The oven as set forth in claim 1, wherein said inner conductor issolid.

4. The oven as set forth in claim 1, wherein the dif ference between thelengths of said electrically conductive members is not greater than onehalf of the wave length of the operating frequency of said generator.

5. In an electronic oven, structure defining a cooking cavity forheating both thawed foods wherein the water content thereof is in theliquid state and frozen foods wherein the water content thereof is inthe solid state, a generator for generating high frequencyelectromagnetic wave energy, a transmission line coupling said generatorto said cooking cavity and including a hollow outer conductor and aninner conductor, said inner conductor including two spaced-apartsections terminating in a pair of spaced-apart ends providing a gapbetween said generator and said cooking cavity of a predeterminedlength, a support member extending into said gap and being movablebetween a first position and a second position, two electricallyconductive contact members of different lengths not less than saidpredetermined length mounted on said support member, and drive means formoving said support member between said first position and said secondposition, one of said contact members being connected to said innerconductor section ends when said support member is in said firstposition for essentially phase matching said generator and said cookingcavity when thawed foods are disposed in said cooking cavity, the otherof said contact members being connected to said inner conductor sectionends when said support member is in said second position for essentallyphase matching said generator and said cooking cavity when frozen foodsare disposed in said cooking cavity, whereby movement of said supportmember by said drive means between said first position and said secondposition serves to accomplish a proper phase matching between saidgenerator and said cooking cavity both when thawed foods are disposedtherein and when frozen foods are disposed therein.

6. The oven as set forth in claim 5, wherein one of said contact membersis mounted on said support member adjacent to one end thereof and theother of said contact members is connected to said support membe rintermediate the ends thereof and said drive means is connected to saidsupport member adjacent to the other end thereof.

7. The oven as set forth in claim 5, and further including an outerconductor section attached to said outer conductor and extendingoutwardly therefrom and accommodating said support member therein.

8. The oven as set forth in claim 5, wherein said drive means includes asource of electric current and a solenoid electrically coupled to saidsource and mechnically coupled to said support member.

9. In an electronic oven, structure defining a cooking cavity forheating both thawed foods wherein the water content thereof is in theliquid state and frozen foods wherein the water content thereof is inthe solid state, a generator for generating high frequencyelectromagnetic wave energy and having a pair of output terminals, atransmission line coupling said generator to said cooking cavity andincluding a hollow outer conductor coupled to one terminal of saidgenerator and an inner conductor coupled to the other terminal of saidgenerator, said inner conductor including two spaced-apart sectionsterminating in a pair of spaced-apart ends providing a gap between saidgenerator and said cooking cavity of a predetermined length, anelongated rod extending through said gap normal to the longitudinal axisof said transmission line adjacent to said gap and being movable betweena first position and a second position, a first electrically conductivecontact member having a first length slightly greater than said gaplength and mounted on said rod intermediate the ends thereof, said firstcontact member bridging said gap when said rod is 'in said firstposition for essentially phase matching said generator and said cookingcavity when thawed foods are disposed in said cooking cavity, a secondelectrically conductive contact member having a second length exceedingsaid gap length by a length no greater than one-half of the wave lengthof the operating frequency of said generator and mounted on said rodadjacent to one end thereof, said second contact member bridging saidgap when said rod is in said second position for essentially phasematching said generator and said cooking cavity when thawed foods aredisposed in said cooking cavity, and drive means connected to said rodadjacent to the other end thereof for moving said rod between said firstand said second positions, whereby movement of said rod by said drivemeans between said first position and said second position serves tochange the effective electrical length of said transmission line toaccomplish a proper phase matching between said generator and saidcooking cavity both when thawed foods are disposed therein and whenfrozen foods are disposed therein.

10. The oven as set forth in claim 9, wherein said second contact memberis substantially U-shaped and has a bight connected to said supportmember and a pair of legs extending toward said gap substantially normalto the axes of said inner conductor sections, the free ends of said legsrespectively contacting said inner conductor section ends when said rodis in said second position.

11. The oven as set forth in claim 9, wherein said rod is axiallymovable.

12. The oven as set forth in claim 9, wherein both said outer conductorand said inner conductor have a rectangular cross section.

13. The oven as set forth in claim 9, wherein said outer conductor has apair of openings therein coaxial with each other and with said gapaccommodating said rod therethrough, and further including two housingsconnected to said outer conductor and extending outwardly therefrom andrespectively overlying said openings therein and respectivelysurrounding said second contact member and said drive means.

14. The oven as set forth in claim 9, wherein the length of said secondcontact member exceeds said gap length by a length in the range fromabout one-tenth of the wavelength of the operating frequency of saidgenerator to about four-tenths of that wavelength.

15. In an electronic oven, structure defining a cooking cavity forheating both thawed foods wherein the water content thereof is in theliquid state and frozen foods wherein the water content thereof is inthe solid state, a generator for generating high frequencyelectromagnetic wave energy and having a pair of output terminals, atransmission line coupling said generator to said cooking cavity andincluding a hollow outer conductor coupled to one terminal of saidgenerator and an inner conductor coupled to the other terminal of saidgenerator, said inner conductor including two spaced-apart sectionsterminating in a pair of spaced-apart ends providing a gap between saidgenerator and said cooking cavity of a predetermined length, anelongated rod extending through said gap normal to the longitudinal axisof said transmission line adjacent to said gap and being movable betweena first position and a second position, a first electrically conductivecontact member having a first length not less than said gap length andmounted on said rod adjacent to one end thereof, said first contactmember bridging said gap when said rod is in said first position foressentially phase matching said generator and said cooking cavity whenthawed foods are disposed in said cooking cavity, a second electricallyconductive contact member having a second length exceeding said gaplength by a length no greater than one-half of the wavelength of theoperating frequency of said generator and mounted on said rodintermediate the ends thereof, said second contact member bridging saidgap when said rod is in said second position for essentially phasematching said generator and said cooking cavity when frozen foods aredisposed in said cooking cavity, and drive means connected to said rodadjacent to the other end thereof for moving said rod between said firstand said second positions, whereby movement of said rod by said drivemeans between said first position and said second position serves tochange the effective electrical length of said transmission line toaccomplish a proper phase matching between said generator and saidcooking cavity both when thawed foods are disposed therein and whenfrozen foods are disposed therein.

16. The oven as set forth in claim 15, wherein both said outer conductorand said inner conductor have a circular cross section.

17. The oven as set forth in claim 15, wherein said outer conductor hasan opening therein accommodating said rod therethrough and furtherincluding an outer conductor section attached to said outer conductorand extending outwardly therefrom and surrounding said second contactmember.

18. The oven as set forth in claim 17, and further including a housingconnected to said outer conductor section at the outer end thereof andextending outwardly therefrom and surrounding said drive means.

19. The oven as set forth in claim 15, wherein said second contactmember is substantially U-shaped and has a bight connected to said rodand a pair of legs extending toward said gap substantially normal to theaxes of said inner conductor sections, the free ends of said legsrespectively contacting said inner conductor section ends when said rodis in said second position.

20. The oven as set forth in claim 15, wherein the length of said secondcontact member exceeds said gap length by a length in the range fromabout one-tenth of the wavelength of the operating frequency of saidgenerator to about four-tenths of that wavelength.

21. The combination for use in an electronic oven and the likecomprising, a transmission line for transmitting high frequencyelectromagnetic wave energy of a predetermined frequency and including ahollow outer conductor and an inner conductor, said inner conductorhaving an insulating gap therein of a predetermined length, andtwo-position bridging means including two electrically conductivecontact members of different lengths not less than said predeterminedlength, said bridging means in the first position thereof bridging saidgap with one of said conductive members and said bridging means in thesecond position thereof bridging said gap with the other of saidconductive members, whereby changing the position of said bridging meansserves to change the effective electrical length of said transmissionline to accomplish a shifting of the phase of the high frequencyelectromagnetic wave energy transmitted therealong.

22. The combination for use in an electronic oven and the likecomprising, a transmission line for transmitting high frequencyelectromagnetic wave energy of a predetermined frequency and including ahollow outer conductor and an inner conductor, said inner conductorhaving a gap therein of a predetermined length, an elongated rodextending through said gap normal to the longitudinal axis of saidtransmission line adjacent to said gap and being movable between a firstposition and a second position, a first electrically conductive contactmember having a first length slightly greater than said gap length andmounted on said rod intermediate the ends thereof for bridging said gapwhen said rod is in said first position, a second electricallyconductive contact member having a second length exceeding said gaplength by a length no greater than onehalf of the wavelength of saidpredetermined frequency and mounted on said rod adjacent to one endthereof for bridging said gap when said rod is in said second position,and drive means connected to said rod adjacent to the other end thereoffor moving said rod between said first and said second positions,whereby movement of said rod by said drive means between said firstposition and said second position serves to change the effectiveelectrical length of said transmission line to accomplish a shifting ofthe phase of the high frequency electromagnetic energy transmittedtherealong.

23. The combination for use in an electronic oven and the likecomprising, a transmission line for transmitting high frequencyelectromagnetic wave energy of a predetermined frequency and including ahollow outer conductor and an inner conductor, said inner conductorhaving a gap therein of a first predetermined length, an elongated rodextending through said gap normal to the longitudinal axis of saidtransmission line adjacent to said gap and being movable between a firstposition and a second position, a first electrically conductive contactmember having a first length not less than said gap length and mountedon said rod adjacent to one end thereof for bridging said gap when saidrod is in said first position, a second electrically conductive contactmember having a second length exceeding said gap length by a length notgreater than one-half of the wavelength of said predetermined frequencyand mounted on said rod intermediate the end thereof for bridging saidgap when said rod is in said second osition, and drive means connectedto said rod adjacent to the other end thereof for moving said rodbetween said first and said second positions, whereby movement of saidrod by said drive means between said first position and said secondposition serves to change the effective electrical length of saidtransmission line to accomplish a shifting of the phase of the highfrequency electromagnetic energy transmitted therealong.

References Cited UNITED STATES PATENTS 6/1969 Di Piazzo 33373

